1. Field of the Invention
The present invention relates to a method and apparatus for mirror-polishing, for example, the outer periphery of a disc-shaped semiconductor wafer and the chamfered portion of the outer periphery of the wafer.
2. Description of the Related Art
Disc-shaped semiconductor silicon wafers (hereinafter, referred to as semiconductor wafers) having a relatively large diameter are subjected to mirror-polishing not only on the surface of them but also on the outer periphery thereof and on the chamfered portion formed to the outer periphery in a manufacturing process, and the reduction of the yield of the wafers due to powder dust deposited on them is prevented thereby.
The outer periphery of wafers has been mirror-polished by the method disclosed in, for example, Japanese Unexamined Patent Publication No. 64-71656 or Japanese Unexamined Patent Publication No. 64-71657.
That is, the chamfered portion of the outer periphery of a semiconductor wafer is mirror-polished in such a manner that the semiconductor wafer is held with a suction chuck or the like and the chamfered portion is pressed against the outer periphery of a polishing drum having an abrasive cloth wound around the surface thereof while rotating the polishing drum at a prescribed speed.
In the above conventional mirror-polishing method, however, there is a problem that a long time is required for the mirror polishing and working efficiency is low because the chamfered portion of the outer periphery of the semiconductor wafer is in line-contact with the abrasive cloth wound around the polishing drum and it is polished under conditions wherein the contact region of the wafer is very narrow.
Further, when the outer periphery of the semiconductor wafer has chamfered portions on both the sides thereof, it is impossible to polish both sides at once. Therefore, after one of the chamfered portions is polished, the semiconductor wafer must be removed from the suction chuck and the other of the chamfered portions must be polished after the semiconductor wafer is reversed and rechucked, which is a troublesome job and by which productivity is lowered.
An object of the present invention, which was made to solve these problems, is to provide a polishing method and apparatus for polishing the outer periphery of a disc-shaped workpiece in order to increase polishing efficiency and to greatly improve productivity by increasing the region where the outer periphery of the workpiece is in contact with an abrasive cloth as well as by continuously and easily polishing a chamfered portion, even if the workpiece has the chamfered portion on both the sides of it.